26 THE VEGETABLE CELL IN GENERAL. 



know them to be organs and even organisms. Histology there- 

 fore begins with the cell in its independent condition. 



117. A complete and living vegetable cell consists of a cell- 

 wall enclosing certain essential contents. 



118. In their earliest state some of the lower plants exist as 

 a mass of motile living matter, not bounded by any envelope. 

 But in all plants of the higher grades the living matter of the 

 cell is from the very first protected by a cell- wall. 



119. That which is essential to the vital activity of a cell is an 

 apparently half-solid substance, protoplasm. With the prop- 

 erties of protoplasm as a living thing. Physiology and not His- 

 tology is immediately concerned. But it is necessary throughout 

 the Itudy of Histology to make a distinction between the cells 

 which are vitally active and those which serve chiefly or wholly 

 some mechanical end ; and hence attention must be called at the 

 outset to the means by which the living matter of the cell can be 

 identified. 



120. Protoplasm exists in all young "cells for instance, in 

 the soft cone of tissue in buds, in root-tips, and other points of 

 growth as a nearly transparent or finely granular substance. 1 

 It completely fills the interior of very young cells, but with 

 increase of the cells in size there arise cavities (vacuoles) con- 

 taining sap, and these by their enlargement and continence may 

 appear to occupy the entire space within the cell. If, however, 

 such a cell be acted upon by anything which causes contraction 



(2) Make a thin section through the petiole of a begonia or some common 

 house-plant, and observe the granules imbedded in the protoplasm (chlorophyll- 

 yranules) ; notice also crystals, either in masses or single. 



(3) Examine a thin section through diy pine wood, test with iodine, and 

 observe the absence of protoplasmic matters. Examine in the same way any 

 hard wood. 



(4) Make a section through any starchy seed, for instance a common bean, 

 and treat it with a solution of iodine ; notice the distribution of protoplasmic 

 matters in the form of thin irregular films throughout the cells. Examine a 

 similar section in oil, and see what differences, if any, can be detected. Prob- 

 ably the presence of protein granules will be made out 



From these preliminary examinations a beginner will have demonstrated 

 the protoplasmic matter in its' active, resting, and reserve states ; he will have 

 seen chlorophyll, the nucleus, and starch, the chief form in which food is 

 stored in plants. He will also have seen a few of the more common crystals. 



After such a study the student is urged to examine practically the charac- 

 teristics of the cell-wall and the cell-contents as they are presented in this 

 chapter. 



1 By the use of staining agents, especially hsematoxylin, protoplasm can in 

 many cases be shown to possess a complicated mesh of very delicate fibres, 



